Tough. More light for the D2, but also more backscatter due to strobe positioning or if you position it to minimize backscatter you will likely get shadows and uneven lighting with just 1.
Do you have a wide angle lens? If you do not, I would get the D2. Using the 01, you’ll need to be way closer for the strobe light to reach your subject since it can’t go as bright as the D2 and if you don’t have a wide angle lens, you won’t be able to capture as much as you may have originally wanted. Subjects and wide scenes will be cut off.
The D2 will be more future proof....you’ll be happier with light output in the long run. When you can afford it, get a second one.